Animals urinate in the same amount of time...
I learned that (almost) all mammals take the same amount of time to urinate from a book of facts.
All mammals that weigh more than about six-and-a-half pounds take about the same time to urinate, thanks to the structure of the urethra. Karen Hopkin reports
But today I learned that mammals also defecate in the same amount of time!
What else did we learn? Bigger animals have longer feces. And bigger animals also defecate at higher speed. For instance, an elephant defecates at a speed of six centimeters per second, nearly six times as fast as a dog. The speed of defecation for humans is in between: two centimeters per second.
Together, this meant that defecation duration is constant across many animal species – around 12 seconds (plus or minus 7 seconds) – even though the volume varies greatly. Assuming a bell curve distribution, 66 percent of animals take between 5 and 19 seconds to defecate. It's a surprisingly small range, given that elephant feces have a volume of 20 liters, nearly a thousand times more than a dog's, at 10 milliliters. How can big animals defecate at such high speed?
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Putting the length of feces together with the properties of mucus, we now have a cohesive physics story for how defecation happens. Bigger animals have longer feces, but also thicker mucus, enabling them to achieve high speeds with the same pressure. Without this mucus layer, defecation might not be possible. Alterations in mucus can contribute to several ailments, including chronic constipation and even infections by bacteria such as C. difficile in the gastrointestinal tract.
Beyond simply following our scientific curiosity, our measurements of feces have also had some practical applications. Our defecation data helped us design an adult diaper for astronauts. Astronauts want to stay in space suits for seven days, but are limited by their diapers. Taking advantage of the viscosity of feces, we designed a diaper that segregates the feces away from direct contact with skin. It was a semifinalist in the NASA Space Poop Challenge earlier this year.
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